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PRAIRIE   DOGS                                    465

Arctomys,; the molars are five in the upper and four in the lower
jaw. The caecum is relatively speaking very small; the measure-
ments in a specimen of & tredecimli'neatiJiS, dissected by Dr.
Tullberg, were; small intestine, 580 mm. ; large intestine, 170
mm.; and caecum, 2 7 mm. In Tamias also the caecum is not
greatly developed. These animals are burrowing in habit.

The Prairie-dogs, genus Cynomys, of which the best-known
species is perhaps G ludouicianus, are very like the Squirrels, but
they are not arboreal creatures; they live in burrows on the
ground, as their vernacular name denotes. The genus is entirely
Itforth American, and four species have been differentiated.

The Prairie-dog or Prairie-marmot is some 10 inches to one

FIG. 233.I^ong-tailed Marmot.   Arctomys caudixtus.     x ^k
foot in length. The tail is no more than 2 inches. The ears
are very small; the thumb is fully developed and bears a claw.
The measurements of the various sections of the intestine are the
following :---Small intestine, 860 mm.;  large intestine, 690 mm.;
caecum, 75 mm. Thus the caecum is not large comparatively
speaking. These animals dig burrows on grassy plains -which
they share with the Ground Owl (Speotyto vunicularis) and with
Battlesnakes, all three species appearing to live in perfect amity.
Probably the Owls use the conveniently-constructed burrows, and
the Rattlesnakes come there to look after the young of both.
Closely allied to the  last  are  the Marmots, genus ^irctomys.
They differ in the rudimentary character of the thumb and in the
longer  tail     The eyes and ears are smalL     The  distribution  of
the genus is Kearctic and Palaearctie.     There are ten species o"f
YOI* X                                                                          2 H